But years ago, Minnesota lawmakers tried banning modifications allowing firearms to shoot faster — to no apparent effect. And some gun-control advocates say banning bump stocks wouldn't even matter. Let's look at how the devices work, their legal status and what they mean in today's gun control debate.

How a bump stock works

To understand how these once-obscure devices work, let's start with some definitions.

Rapid-fire guns come in two basic varieties: semi-automatic and fully automatic. Semi-automatic guns will fire one bullet for each pull of the trigger. They're legal and common in gun cabinets all over Minnesota.

Frankie McRae illustrates the grip on an AR-15 rifle with a bump stock.

Allen G. Breed | AP

Fully automatic rifles, however, fire continuously while the trigger is held. Minnesota and federal law tightly regulate fully automatic weapons — known better as machine guns.

Bump stocks are used on semi-automatic guns to speed up the two-step process for firing: squeezing, then releasing the trigger. The devices allow the trigger finger to stay in place while the part of the gun against the shoulder uses the recoil to fire repeatedly — similar to a fully automatic rifle.

What does the law say?

In Minnesota, there's a law on the books that specifically bans trigger activators, which speed up a gun's rate of fire. The measure has been in place since 1993, the year of the Branch Davidian siege in Waco and a shooting in San Francisco that killed eight people. Both of those events involved trigger adaptations to speed up semi-automatic firearms — like a bump stock does.

State Sen. Dick Cohen, DFL-St. Paul, sponsored the bill years ago. He said bump stocks should be banned by law.

"That's no question that would have been the intent years ago to have done that, to make sure that the tragedy of Las Vegas years later, would not have happened in Minnesota," Cohen said on Thursday.

But years after the '93 law, Texas-based Slide Fire offered the federal Bureau of Alcohol, Tobacco, Firearms and Explosives its patented bump stock for review. Slide fire got approval for the device in 2010, during the Obama administration.

There's no indication anyone in Minnesota has addressed the legality of the bump stock under state law or initiated any prosecutions. A spokesperson for the Bureau of Criminal Apprehension, which has limited jurisdiction regarding machine guns, said her agency hadn't issued any written direction about the devices.

There may be many bump stocks in Minnesota now — they were widely available for sale on the internet until Slide Fire stopped taking orders Thursday afternoon.

How are bump stocks playing out in the gun control debate?

Sen. Dianne Feinstein, D-CA, center, has introduced legislation that would ban devices that could make weapons fully automatic.

Chip Somodevilla | Getty Images

The NRA has asked the Bureau of Alcohol, Tobacco, Firearms and Explosives to review its stance on bump stocks.

However, gun control advocates don't think the NRA's statement or congressional opposition to bump stocks is serious.

The Rev. Nancy Nord Bence is executive director of Protect Minnesota, a state-based gun violence prevention group. She believes federal officials aren't in any position to recind approval for the devices. And she said other modifications, like so-called echo triggers that fire on both pull and release, will continue to offer gun owners machine-gun like rates of fire anyway.

"All this does is give Republicans a place to go now. To say, 'Oh, yeah, we're supporting this idea that we're going to review these,'" she said. "It's not going to change anything."

Some gun owners themelves sound indifferent to the fate of bump stocks. Rob Doar, political director with the Minnesota Gun Owners Political Action Committee, said his organization isn't taking a position on the devices.

Many gun owners find them ineffective and wasteful for serious shooting, he said.

"We're kind of struggling because it's one of those things that it's kind of like a spoiler on a car. They really don't serve any purpose," Doar said. "They're just kind of one of those things that somebody created in their garage probably one day, and thought hey, this might be fun. And now somebody abused it and here we are."